Torque wrench



May 14, 19 6. F. w. Llvl-:RMoNT f y 2,400,205v

v TORQUE WRENCH l v 1 Filed March 1, 1943 f2 14152634: f ,24 .a6 i z5 23 M 532- l@ Mfw Patented May 14,` 1946 UNITED STATES PATENT OFFICE TORQUE WRENCH Application March 1, 1943, Serial No. 477,601

10 Claims.

This invention relates to Wrenches for applying a predetermined measured torque to nuts and bolts and has as a broad object to simplify and increase the accuracy, reliability and service life of such wrenches.

The present wrench is a further development of the wrenches disclosed in my application Serial No. 468,793, filed December 12, 1942, issued March 20, 1945, Patent No. 2,371,901, which relate to torque wrenches of the snap-action typev employing snap-action springs as distinct from the prior art devices employing cam mechanisms. The present Wrench differs in detail from those disclosed in my prior application and has advantages in simplicity and reliability- A feature of the present invention is a torque wrench having a handle member and a head member which are readily separable to provide for the rapid interchange of different sized heads.

Essentially the present wrench comprises a handle to which there is pivotally connected a head member adapted to be attached to the nut to be tightened, with a pair of springs within the handle for yieldably resisting 'rocking movement of the handle with respect to the head. One of the springs is of the bar type, is relatively stiff,

and provides most of the resistance to relative movement between the handle and the head. The other spring is of the thin strip type which is normally bowed in one direction but which is so stressed during rocking movement of the handle with respect to the head as to rever-se its curvature with a sudden snap when the applied torque exceeds a predetermined value.

A full understanding of the construction may be had from the detailed description to follow, which refers to the drawing.

In the drawing:

Fig. 1 is a longitudinal sectional View through a wrench in accordance with the invention, the wrench being shown in its position of rest.

Fig. 2 is a longitudinal section taken at right angles to the section of Figure 1 and substantially along the line II--II of Figure 1. h

Fig. 3 is a face View of the snap spring element of the wrench.

Fig. 4 is a View similar to Figure 1 but showing the Wrench stressed just to the point where it applies the maximum torque for which it is adjusted.

Fig. 5 is a View similar to Figure 4 but showing the wrench just as the set torque has been exceeded and the snap spring has reversed its position; and

. Fig. 6 is a side elevation of a wrench head of different dimension-s for use in the wrench of Figures 1 to 5.

Referring first to Fig. 1, the wrench therein disclosed comprises a head It adapted to engage the nut or other object to be turned, which head is removably associated with a handle II. The handle I I consists of a hollow shell of rectangular cross section, relatively thin as compared with its width, as is apparent from comparison of Figs. landv 2. The head IG has an end portion insertab'le into one end of the handle II and pivotally engageable with a pair of stub shafts I2, which lare secured to opposite side walls I3 of the handle and project inwardly toward each other. The juxtaposed faces of the stub shafts I2 are spaced apart a distance slightly greater than the thickness of a web por-tion It of the head lill, the sides of the inner portion of the head being recessed to define this web i4. The recesses `are in the form of longitudinal .grooves rounded at the inner end to .define pivotal seats I5 which bear against the stub shafts I2 during rotation of the handle II with respect to the head -I d. The seats i5 are slightly offset from the `grooves -so that while the head can be pressed into the handle or removed therefrom, the head is yieldably reta-ined in position by cooperation between the offset seats I5 and a main spring i6 within the handle.

The main spring I6 is a bar spring rigidly supported at one end from the handle II by an anchor block ITI, the latter having a longitudinal hole `i8 into which the rear end `of the spring ILE pressed and locked in place by a pair of trans-verse pins- I9 placed into holes provided therefor -in the bloc-k -I'I andthe spring I6. The block Il" is slidable in the handle II for assembly but is locked in posi-tion with a screw 20. The head of the screw 20 is purposely permitted to project from the edge of the handle II to serve as an indication to the user of the direction in which the wrench `is to be moved. Thus, the wrench as shown Fig. 1 is to be used to apply clockwise torque to a nut by the application of force to the upper edge of the wrench handle.

It will-be observed from Fig. 1 that the lower side of the left, free end of the bar spring I6 bears against an arm -2I on the inner end of the head I0, urging this arm downwardly so that a flat face 22 on the edge ofthe head bears against the edge wall 23 of the handle, in which position of the head the seats I5 therein rest against the pivoting stub shafts I 2. The upper face of the arm V21 is preferably rounded to provide for line contact with the bar spring I6 at a point displaced from the end of the arm. It will be apparent from the construction shown and described that the head IU can be removed by forcing it up, thereby slightly deflecting the bar spring i6, and then pulling it straight out. The same or a similar head of another size can be reinserted by reversing the procedure.

The spring mechanism of the wrench includes in addition to the bar spring IS a relatively thin strip spring 24 which extends approximately parallel to the spring I6 and is supported at one end from the handle I l and at the other end fro-m the bar spring I6. Referring to Fig. 3, the strip spring 24 has a notch 25 at its right end and a window 26 near its left end and it is reenforced adjacent the window by a short reinforcing strip 27 (Fig. l) which extends along the under side of the spring 24 and is folded around the end of the spring. It may be spot welded to the spring 24 where it is folded around the end of it. The notch 25 at the right end of the spring is engaged by a notch in the end of a supporting pin 2S slidably mounted in a longitudinal hole 29 provided therefor in the block Il, The outer end of the hole 29 is threaded to receive an adjusting screw 3u, the inner end of which bears against the pin 28. To lock the screw 30 in a position of adjustment, a transverse slot 3| is provided in the block I'l leaving a flexible segment 32 of the block which can be urged against the main portion of the block by a locking screw 33. The screw 33 can be adjusted to provide sufficient resistance to rotation of the screw 30 to hold the latter in a position of adjustment although permitting it to be intentionally turned with a screwdriver. The strip spring 24 is supported at its forward end by engagement of an integral hook 34 on the bar spring I6 with the rear edge 35 of the window 26, this window extending through the reenforcing strip 21 as Well as through the strip spring 24.

The strip spring 24 is normally slightly bowed, as shown in Fig. 1, so that it is concave on its upper side and an indicator pin 36 on the spring is positioned below a window 3l in the upper edge wall 33 of the handle ll. The pin 28 is so adjusted as to exert slight longitudinal force on the strip spring when the wrench is in the inactive position shown in Fig. 1. As torque is applied to the handle I I to tighten a nut 39 (Fig. 4) to which the wrench head is affixed, the bar spring I6 yields to permit rocking movement of the handle with respect to the head. During the initial portion of this rocking movement the only resistance is that offered by the bar spring I6 but continued movement carries the left reenforced end of the strip spring 24 against an adjustable stop screw 4U mounted in the edge wall 33 so that further movement is in part resisted by the strip spring, which becomes distorted. Thus, referring to Fig. 4, the downward force exerted on the left end of the strip spring by the stop screw 40 tends to rock the left end portion of the strip spring counterclockwise about the hook 34 as a fulcrum, which places a reverse bend in the spring. As shown in Fig. 4, this movement has been carried to a point where the strip spring is about to snap over into a simple bow as shown in Fig. 5. In the latter position the indicating pin 36 is projected through the window 3l and would impinge against a finger of the operator using the wrench, thereby indicating to him that the torque for which the wrench was adjusted has been exceeded. The reverse movement of the spring from the position sho-wn in Fig. 4 to that shown in Fig. 5 occurs very suddenly and is accompanied by a clearly audible snapping sound which would indicate to the operator that the desired torque has been applied even though the operators fingers should happen to be positioned clear of the Window 3T.

As the wrench moves from the position shown in Fig. 4 to that of Fig. 5, the torque applied from the handle to the wrench head is momentarily reduced by virtue of the fact that beyond the point of snap-over illustrated in Fig. 4 the strip spring 24 ceases to aid the bar spring l 6 in resisting the rocking movement of the handle with respect to the head. It is desirable that the torque be reduced after the set value thereof is passed to prevent the accidental application of additional torque.

The Wrench is adjustable to cover a relatively wide range of torques by adjustment of the stop screw 4U and by substituting heads of different dimensions. The torque can be adjusted within a range extending approximately fty percent in either direction from a middle value by adjustment of the stop screw 40. If a larger variation is desired, it should be obtained by substituting a head l] of different dimensions.

Variations in the torque setting may be obtained by changing the dimensions of the head lil in either of two Ways. One way is to lengthen the arm 2| so that it contacts the bar spring I6 nearer the base of the latter. Obviously in order to produce the same deflection of the bar spring I6, a force applied to the latter near the base must be much greater than force applied near the tip. Very large variations in the torque at which the wrench trips can be had by varying the length of the arm 2| on the head.

Obviously the torque applied to a nut engaged by the head l) can be varied by varying the distance between the seat l5 and the center 45 of the nut engaging portion of the wrench, since this increases the llength of the lever arm,

There is shown in Fig. 6 a wrench head lila adapted for use on larger nuts than the head lil. Usually larger nuts require a larger torque to properly tighten them and in this instance the head lila is adapted to apply a larger torque by making it longer on both sides of the seat I5 than is the case with the head if! of Figs. l to 5.

It is easily possible by suitably choosing the length of the head to vary the torque at which the wrench trips from values as low as 10 inchpounds to values as high as G inch-pounds.

The vigor of the snap of the strip spring 24 can be varied between rather wide limits by adjusting the longitudinal compression with the screw 3i). This adjustment also determines the extent to which the applied torque is reduced at the instant of snap-over. It is found desirable to have a torque reduction of approximately twenty percent when snap-over occurs. The extent of this reduction can be varied between any limits desired by varying the relative stiffness of the strip spring 24 and the bar spring I6. v

Ready adjustment of the vigor of the snap action of the strip spring is desirable because one operator, such as a husky man with calloused hands, might desire a relatively strong kick by the pin 36 whereas a relatively delicate Woman worker would be afraid of the tool were it adjusted to give too violent a kickf Various changes can be made from the exact construction disclosed in the drawing without departing from the invention and the latter is,

therefore, to be limited only to the extent set forth in the appended claims.

I claim:

l. In a torque wrench, a work engaging head member, a handle member, means rockably intercoupling said members, and spring means interposed bettveen said members for. yieldably resisting rocking movement therebetween, said spring means comprising: a spring strip having a transverse shoulder adjacent to but spaced from one end thereof, first and second strip-supporting elements adapted to bear against said shoulder and against the other end of said strip respectively and compress said strip longitudinally therebetween, said strip being normally curved longitudinally so that it is concave on one side, means for laterally moving said one supporting element in the direction of the concave side of said strip in response to rocking movement between said handle and head members, and a stop member for contacting said one end of said strip and limiting lateral movement thereof whereby continued movement of said one supporting element reverses the longitudinal curvature of 'said strip with a snap action.

2. A wrench as described in claim 1, in which said one end portion of said strip is reinforced to reduce flexing of said spring adjacent said shoulder.

3. A wrench as described in claim 1, in which said first strip-supporting element comprises a spring bar anchored at one end to said handle `member and in which said second supporting member is anchored to said handle member adjacent the point of anchorage of said spring bar.

4. In a torque wrench, a work engaging head member, a handle member, means rockably intercoupling said members, and spring means interposed between said members for yieldably resisting rocking movement therebetween, said spring means comprising a spring strip having a transverse shoulder adjacent to but spaced from one end thereof, first and second strip supporting elements adapted to bear against said shoulder and against the other end of said strip respectively and compress said strip longitudinally therebetween to bow it longitudinally so that it is concave on one side, and means for laterally moving said one supporting element in the direction of the concave side of said strip in response to rocking movement between said handle and head members, a stop member for contacting said one end of said strip and limiting lateral movement thereof, whereby continued movement of said one supporting element reverses the longitudinal curvature of said stripping spring with a snap action, and means for varying the longitudinal compression of said strip to vary the vigor of said snap action.

5. In a torque wrench, a work-engaging member, a handle member, means for rockably connecting the work-engaging member with the handle member at one end thereof, a spring beam, means for anchoring the spring beam within the handle member at a point spaced from the said rockable connecting means, the spring beam member extending towardk the work-engaging member, the work-engaging member having a pressure arm adapted to engage the free end of the spring beam, a snap member mounted within the handle member and operatively connected with the free end of the spring beam so as to be reversely actuated when the force exerted through the handle member to the workengaging member causes said spring beam to be deflected beyond a predetermined amount and when said force is released.

6. A torque wrench, comprising: a handle member; a work-engaging member including a pressure arm and a work-engaging head; a spring beam anchored in said handle and having a free end engageable with said pressure arm; separable journal means for said work-engaging member located between said head and said pressure arm, said journal means including a pivot shaft in said handle member and pivot seat means in the form of longitudinally extending laterally recessed guide surfaces on the sides of the work-engaging portions adapted to receive said pivot shaft means, said spring beam adapted to bear on said pressure arm to seat said pivot shaft means in the laterally recessed portions of said pivot seat means.

7. A torque wrench, comprising: a handle member having a recess in one end; a tool element including a work-engaging head and an arm extending therefrom, the length of the arm being proportioned to the size of the Workengaging head; separable journal means for fulcruming said tool element in said handle with its head protruding therefrom; and a cantilever spring beam anchored in said handle and extending into engagement with the arm of the tool element inserted in said head, the length of the arm of said tool element between said journal means and its engagement with said spring beam being determinative of the pressure required to deflect said spring beam.

8. A construction as set forth in claim 7, wherein: said journal means includes a pair of coaxial stub pivots projecting into said handle from the sides thereof, coacting journal seats depressed in the sides of said tool element, and axially accessible communicating with said seats and adapted to receive said pivots as said tool element is inserted into said handle; said spring beam adapted to bear on the arm of said tool element to yieldably hold said pivots in said seats.

9. A torque wrench, comprising: a handle member having a recess in one end; a tool element including a work-engaging head in an arm extending therefrom, the length of the arm being proportioned to the size of the workengaging head; separable journal means for fulcruming said tool element in said handle with its head protruding therefrom; a cantilever spring lbeam anchored in said handle and extending into engagement with the arm of the tool element inserted in said head, the length of the arm of said tool element between said journal means and its engagement with said spring beam being determinative of the pressure required to deflect said spring beam; and an over-center snap spring in said handle positioned to be deflected past its center when said spring beam is deflected beyond a predetermined point; and a tell tale element actuated by said snap spring.

10. A construction as set forth in claim 9, wherein: said journal means includes a pair of coaxial stub pivots projecting into said handle from the sides thereof, coacting journal seats de- Dressed in the sides of said tool element, and axially accessible communicating with said seats and adapted to receive said pivots as said tool element is inserted into said handle; said spring beam adapted to bear on the arm of said tool element to yieldably hold said pivots in said seats.

FRANK W. LIVERMONT. 

